remove .lgtm file, since the service has been discontinued

see https://github.com/tldr-pages/tldr/pull/1173#issuecomment-266788990 and https://github.com/lgtmco/lgtm/issues/56 for details

.lgtm

@@ -1,2 +0,0 @@
-approvals = 2
-pattern = "(?i):shipit:|(?i)LGTM|:\\+1:|:ok_hand:"